If I respond to a debt collection agency does this start the Statute of Limitations all over again?
It depends on what you mean by responding to the debt collection agency. If you are just referring to some sort of communication to interact with the debt collection agency, then that act alone should not restart the Statute of Limitations. What is required to restart the Statute of Limitations is acknowledging the debt, in most states a payment being made is required. However, since you do owe debt, not responding to a debt collector could lead to them suing you and winning a judgment. Your best bet is to try to settle the debt with them, and depending on how much time is left on the Statute of Limitations you could settle for half or less.
Talk to a Debt Settlement Lawyer to find out what legal options you have to handle the debt or settle it for a small amount.